Shared listeners in shared object space

ABSTRACT

A system for sharing listeners monitoring events occurring in objects shared by multiple applications each running inside its own virtual machine in a computer system.

CROSS REFERENCE TO RELATED APPLICATIONS

Not applicable

BACKGROUND OF THE INVENTION

The present invention relates to a system for sharing listener objectsamong multiple applications each running inside its own virtual machine.

Computer hardware and storage media can only create, store, and processbinary information, i.e. information written using only two digits, “0”and “1”. A compact disc, for example, has a surface subdivided into tinysections that are either pitted (1) or not pitted (0) such that a lasercan detect the presence or absence of pits. Similarly, microprocessorshave inputs and outputs to which a reference voltage either is (1) or isnot (0) present. (Microprocessors repeatedly measure the voltage at eachinput and output at regular intervals, or cycles—hence the speed of aprocessor is expressed in cycles per second, or “Hertz.”) Accordingly,any computer program, as well as any data used in that computer program,must first be expressed in binary code for a computer to run the programor process the data.

Though binary code is conceptually simple, its use to performcomputerized tasks introduces two drawbacks. First, binary code is arelatively inefficient way to express information. As a simple example,the number “100” in decimal notation is expressed as “1100100” in binarycode, and therefore must at a minimum occupy seven “pits” on a compactdisc and/or occupy either a single input of a processor for seven cycles(if entered serially) or seven inputs for one cycle (if entered inparallel). In technical terms, the space that a piece of informationoccupies, or alternatively the number of time cycles a piece ofinformation occupies, is referred to in “bits.” That is to say, thenumber “100” is a 7-bit number because it takes seven digits to expressin binary code. The number “101” is also a 7-bit number, coded as1100101, as is every number between “64” (1000000) and “127” (1111111).

In computer applications, binary code is even more inefficient becausecomputerized information is, by convention, typically expressed inmultiples of 8 bits, e.g. 8-bit, 16-bit, 24-bit, etc. The reason forthis convention is that a computer processing or storage device has nophysical way of distinguishing when one number ends and another numberbegins. Accordingly, the convention is to write a program that specifiesthe bit-rate, i.e. the number of bits that each piece of data processedin the program will occupy. If a program is written in 8-bit code, forexample, every piece of data occupies eight bits, e.g. the number 0 iscoded as 00000000, the number 1 is coded as 00000001, and the number 255is coded as 11111111. In 8-bit code, therefore, every piece of data hasa value between 0 and 255 and every piece of data occupies 8 bits evenif it could theoretically be represented by a single bit. If a programrequires that any piece of data take on a value greater than 255, thebit-rate for the program must be increased incrementally to 16-bit,24-bit, etc. as appropriate.

A computer program operating in binary code may therefore use atremendous amount of storage space and processor cycles, particularlywhen graphics are involved. For example, a photographic quality image isoften coded at 24-bits for every pixel. If the image resolution is 2million pixels, as is common with today's digital cameras, each imagewould occupy 48 million bits, or 4 Megabytes, where a byte is defined as8 bits per byte (due to the convention of expressing binary code inmultiples of 8 bits). Manipulating that image would similarly require 48million cycles of processor time for each manipulation. The amount ofstorage space and processing time increases exponentially whenmanipulating video because the computer system must process and storemany such images every second. In addition, there are many othercomputer applications that are at least as intensive as imageprocessing. Applications of such intensity tend to slow considerably asdata is “bottlenecked” in the computer system.

One way of minimizing the impact of the inefficiency of binary code hasbeen to increase the amount of storage space and processing speed ofcomputers. For example, personal computers sold commercially today offerup to 300 gigabytes (300 billion bytes) of hard drive storage, 4gigabytes (4 billion bytes) of temporary memory storage, and processingspeeds of over 4 gigahertz (4 billion cycles per second). Businesscomputers, such those used in the motion picture industry are evenfaster and include more storage. In other words, as computerapplications have demanded more storage space and processing time, thecomputers have become faster with higher storage capacity. Still, whilethese numbers are impressive, computer systems are not sufficiently fastas to eliminate all bottlenecks, and in fact, as computers become fasterwith more available storage, new applications are developed to takeadvantage of the improved technology so as to provide the need for evenfaster computers, even more storage space, etc.

Another way of minimizing the impact of the inefficiency of binary codeis to write computer programs and applications as efficiently aspossible. Thus there is always an emphasis on writing computer code thatachieves its outcome in as few steps or calculations as possible.Similarly, a computer program should not be written in 24-bit code whenonly 8-bit code is required for the application, and the computerprogram may compress data when appropriate.

A second drawback of using binary code to perform computerized tasks isthat it is impractical to write a computer program in binary code,particularly with complex programs. The first rudimentary computers, forexample, were operated by mechanically toggling electrical switchesbetween on and off states to enter a sequence of binary instructions.Computer programs simply specified the sequence of binary instructionsto enter. This method was feasible so long as the program was no morethan about a hundred instructions long. Beyond that point, programmingdirectly in binary code became too complex, and programs too difficultto correct, or debug. Moreover, because the binary instructions weredependent upon the particular electrical circuitry of the computerprocessor and related hardware, the programmer was required to know indetail the particular architecture of the computer being used by theprogram.

To accommodate computer programs of increasing complexity, as well as tofacilitate the introduction of personal computers into the marketplace,modern operating systems were developed. Early computer operatingsystems, such as Microsoft Corporation's MS-DOS disk operating system(DOS) software, essentially acted as an interface with a computer'shardware so that a user could issue specific commands or instructions tothe computer written in more ordinary language. The operating systemwould recognize the commands, and automatically issue the instructionsto the computer in binary code. For example, in MS-DOS software,entering the command “MEM” into the computer would result in thecomputer displaying the types and amounts of computer memory available.The person issuing the command did not need to know anything aboutbinary code or the manner in which the command being entered producedthe desired result. The user simply needed to either memorize or look upa set of commands in an instruction manual.

Further, early operating systems recognized simple programminglanguages, such as Beginner's All-purpose Symbolic Instruction Code(BASIC) and FORTRAN, written in terms more intuitive than binary code.In these languages, commands such as WRITE, READ, LOOP, SET and otherintuitive terms provided a means to write computer programs in a mannereasily learned and perhaps more importantly, in a manner more easilyreadable when debugging the program. A simple computer program tocalculate the area of a circle, for example, might have been written inBASIC approximately in this form:

10 PROGRAM 1 20 WRITE “This is a program to calculate the area of acircle.” 30 WRITE “Please enter the radius of the circle” 40 READ R 50SET A=Π *R{circumflex over ( )}2 60 WRITE “The area of the circle is” R70 END

In this example, after a person typed “RUN PROGRAM 1”, the computerwould execute the command lines in numerical sequence, whereby a personwould be prompted to enter the value for a radius, defined as “R”, afterwhich the computer would square that value, multiply the squared valueby pi and print out the computed area. Writing this same program inbinary code not only would have required much more time and effort onthe part of the programmer, but the programmer also would have had toknow the technical specifications of the computer processor. Obviously,the introduction of operating systems along with intuitive programminglanguages was a boon to both consumers and computer programmers.

A number of such operating systems and programming languages becameprevalent. For example, Apple Inc.'s MAC OS and Microsoft's WINDOWSoperating systems improved (from a consumer's perspective) upon simpletext-based operating systems such as DOS by allowing a user to issueinstructions to the computer using a point-and-click graphical interfacedisplayed on a computer monitor. Computer applications, such as wordprocessing programs, computer games, and a host of others took advantageof this functionality to provide products that could be used moreintuitively through the graphical interface. Today, a host of operatingsystems are used, such as many versions of the WINDOWS, MAC OS, LINUXand WINDOWS NT software, among others.

A wide variety of programming languages also became prevalent. At first,most new programming languages followed the model of the early FORTRANlanguage by structuring the programming language as a series of commandsby which a programmer would issue instructions to a computer in alogical order. The most popular of these language types is a programcalled “C.” The creation of “C” is considered by many to have marked thebeginning of the modern age of computer languages. “C” successfullysynthesized what had seemed to be conflicting attributes of severalexisting programming languages, adding new attributes to form a single,powerful structured language that also happened to be easy to learn.Moreover, it was a programmer's language. Prior to the development of“C”, computer languages were generally designed either as academicexercises by engineers or designed by bureaucratic committees. “C”,however, was developed by programmers, reflecting the way theyapproached the task of programming. As a result, “C” found wide andrapid acceptance in the programming community, attracting many followerswho had near-religious zeal for it.

Once again, however, the increasing complexity of computer programsexposed an underlying flaw of “C” as well as its predecessors. Each ofthese programming languages requires that a program be written as aseries of linear steps or instructions (with an occasional loop orbranch thrown in). In fact, writing such a program is similar toconstructing a geometric proof, and like a proof, once a program such asC or FORTRAN exceeds a certain number of steps (somewhere between 25,000and 100,000 lines of code), the program becomes too complex to writeeffectively.

Therefore a new approach to computer programming began to findacceptance in the programming community, commonly referred to asobject-oriented programming. Object-oriented programming approaches aprogramming task in roughly the same way that a person's mind mightapproach that task—by abstracting a solution. Rather than defining aseries of steps, or instructions by which a task could be accomplished,an object-oriented program focuses first on a program's data, definingclasses of data and objects, where an object is a particular instance ofa class. An object-oriented program still contains instructions,referred to as methods, which often are embedded within the classes orobjects themselves. An example of a simple object oriented program thatdisplays the volume of two boxes might look like this:

class Box {    double width;    double height;    double depth;    //display volume of a box    void volume ( ) {       System.out.print(“Volume is ”);       System.out.println (width*height*depth);    } }class BoxDemo {    public static void main (String args[ ] {       Boxmybox1 = new Box ( );       Box mybox2 = new Box ( );       // assignvalues to mybox 1's variables       mybox1.width = 3       mybox1.height= 20       mybox1.depth = 15       // assign values to mybox2'svariables       mybox 2.width = 3       mybox2.height = 6      mybox2.depth = 9       // display volume of mybox1      mybox1.volume ( );       // display volume of mybox2      mybox2.volume ( )

In this example program, a box class is first defined having thevariables of width, height, and depth (the term “double” identifies thetype of number that the variable is allowed to be). The box class alsodefines a method to display the volume of an object box of this class bymultiplying width by height by depth. Once this class has been defined,the program defines a second class BoxDemo which includes two objects ofthe initial box class. The class BoxDemo then twice calls the method ofthe first box class for displaying the volume of a box, once to displaythe volume of mybox 1 and once to display the volume of mybox2.

Object oriented programming has quickly gained widespread popularity.One particularly popular object oriented language is called JAVA, whichis the programming language used in the foregoing example. JAVA is aregistered trademark of Sun Microsystems Inc. The reason the JAVAprogramming language has become so popular is its versatility indefining classes and objects, as well as its ability for one class orobject to call functions in other classes and objects as well as toreuse data in other objects simply by referencing the function or thedata. In the JAVA language, therefore, it is very easy to createmultiple variations of a defined class, to create new variations of anold class, and to reuse a method previously defined by one class in anew class. Parenthetically, another object oriented programming languagethat has become popular is C++, which expands C to include thefunctionality of both object oriented programming and the instructionoriented programming of C.

The JAVA language, like any other programming language relies upon aninterface to convert the program to the required binary instructions.With the JAVA programming language, this interface is called a “VirtualMachine” (VM) because the interface behaves as if it were a computerunto itself. Every time a JAVA language based computer application isinitiated, the application initiates a VM to run the application. TheJAVA virtual machine (VM) will be described in much greater detail laterin this specification, but several important principles will beintroduced now. First, while the input to a JAVA VM is always the JAVAprogramming language, the output of a JAVA VM is customized to theparticular platform, or operating system, that hosts the JAVA VM. Inother words, every JAVA application must be customized to the hostoperating system so that the VM that it creates is capable of convertingthe JAVA programming language to the commands unique to the hostoperating system, which in turn issues the appropriate binaryinstructions to the computer.

Second, JAVA VMs are designed to be independent of one another. If twoJAVA applications are running on the same computer, each applicationcreates its own VM which is self sufficient, i.e. neither VM needs relyupon the VM of the other application. If one application should close,the other application will not be affected. This often becomesproblematical, however. Recall that even with today's processors andstorage devices, a computer's resources may still be strained byintensive applications. With multiple JAVA applications runningsimultaneously, each creating its own VM, system resources may bestrained and slowdowns may result. In other words, there is often atrade off between the desired independence of multiple JAVA applicationsand the speed at which the applications may run.

Third, the creators of the JAVA VM, Sun Microsystems, emphasizeduniformity of the JAVA VM with respect to all of the host operatingsystems. Thus, while the “guts” of each VM will of necessity bedifferent across each platform, a user of a JAVA VM was not intended tobe able to recognize any difference, seeing the same functionalityregardless of the host platform. This, however, became problematical.Many operating systems offer unique features not available to otheroperating systems. Thus a business operating on the WINDOWS NT operatingsystem might desire to have a JAVA VM, and hence the JAVA applicationrunning the VM, take advantage of that unique functionality. The samewould hold true for a user of a system with a MAC OS, LINUX, WINDOWS 9×or other operating system. Therefore, although Sun Microsystems' JAVA VMis uniform across all platforms, an industry has blossomed by which JAVAapplications may be truly customized to a host operating system wherebythe features of the host operating system are more fully exploited, andcustom tailored to the particular needs of the business or personrunning the application.

This diversity among JAVA VMs tends to hinder the improvement of theJAVA VM and the programming language because many such improvements aretied to the particular species of JAVA VM upon which the improvement wasdeveloped. Many businesses may like the particular improvement, butdislike other aspects of the JAVA VM. In that instance, a business withits own custom or proprietary VM would have the options of buying thenew VM with its perceived advantages and faults, or spend the time andresources to engineer its own VM, which it likes, to include the newimprovement. Exacerbating this problem is that the new improvement maybe proprietary, thus eliminating the second option.

What is desired then, is an improved system for implementingobject-oriented computer applications that both efficiently allocatescomputer hardware resources among multiple computer applications runningsimultaneously on the same computer or network of computers, or amongmultiple threads of a single computer application running on a computeror network of computers, while also preserving the independence ofmultiple, simultaneous applications. What is further desired is such animproved system that is sufficiently flexible so as to be compatible notonly with the diverse range of existing object-oriented computerapplications, but also with object-oriented applications that aredeveloped or modified in the future.

BRIEF SUMMARY OF THE INVENTION

A computer system for concurrent operation of plural applications isdisclosed comprising a memory, including a shared object space; a sharedobject stored in the shared object space and accessible to at least twoapplications so that at least a first application running in a firstvirtual machine is capable of causing an event in the shared object; anda listener stored in the shared object space, attached to the sharedobject and operably associated with a second application running in asecond virtual machine. The listener listens for the event and notifiesthe second application when the first application has caused the event.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified architectural schematic of an existing VM.

FIG. 2 is an expanded architectural schematic of the VM of FIG. 1showing a memory region interposed between the class loader and theexecution engine.

FIG. 3 is a schematic of the heap shown in FIG. 2.

FIG. 4A is a diagram showing a prior art system for operating multipleVM applications on a host computer.

FIG. 4B is a diagram showing a prior art system for the simultaneousoperation of multiple instances of a VM application on several hostcomputers connected through a network or internet server.

FIG. 5 is a diagram showing a first improved system for operatingmultiple VM applications on a host computer.

FIG. 6 is a diagram showing a first manner in which objects may beshared between applications using the system of FIG. 5

FIG. 7 is a diagram showing a second manner in which objects may beshared between applications using the system of FIG. 5

FIG. 8 is a second improved system for operating multiple VMapplications on a host computer.

FIG. 9 is an improved system for the simultaneous operation of multipleinstances of a VM application on several host computers connectedthrough a network or internet server.

FIGS. 10A and 10B show a system for synchronizing locks on objectsshared in a shared object space.

FIG. 11 shows a system for sharing listeners where a plurality ofapplications may be notified of an event detected by a single listener.

FIG. 12 shows a system for sharing listeners where a listener notifies afirst application of an event caused by a second application.

DETAILED DESCRIPTION

FIGS. 1-4B show a simplified architectural schematic of an existingvirtual machine 10, computer software implementing an abstract computingmachine, and, more specifically, a JAVA virtual machine (JAVA VM),although it should be understood that other types of VMs besides theJAVA VM may also have the features shown in FIGS. 1-4B. Referringspecifically to FIG. 1, when a JAVA application is initiated on a hostcomputer with a host operating system 12, the JAVA virtual machine (VM)10 loads the application which may include a class loader 16 and anexecution engine 18. Although FIG. 1 indicates a single class loader, inactuality, a JAVA VM may include multiple class loaders. Thus the classloader 16 may be considered a subsystem that may involve many classloaders. The JAVA VM 10 has a flexible class loader architecture thatenables a JAVA application to load classes in custom ways.

Specifically, the class loader 16 may comprise a system class loader andone or more user-defined class loaders. The system class loader is apart of the JAVA VM implementation and loads classes, including the JAVAapplication programming interface (API) class files 20, in some defaultway and usually from the local disk of the host computer. As previouslystated, the particular default manner in which the system class loaderloads classes is specific to the particular VM implementation being usedand may be customized. The term “system class loader” is sometimesreferred to as a “primordial class loader”, a “bootstrap class loader”,or a “default class loader.”

At run time, a JAVA application may also load application class files 22in custom ways through user-defined class loaders, such as bydownloading class files across a network. While the system class loaderis an intrinsic part of the VM implementation, the user-defined classloaders are not. Instead, user-defined class loaders are written in theJAVA programming language, compiled to class files, loaded into thevirtual machine, and instantiated just like any other object, becoming apart of the executable code of a running JAVA application. User definedclass loaders enable a programmer to dynamically extend a JAVAapplication at run time. As the application runs, it can determine whatextra classes are needed and load them through one or more user-definedclass loaders. Because the user defined class loaders are written in theJAVA language, classes can be loaded in any manner expressible in theJAVA programming language.

For each class loaded by the virtual machine 10, the virtual machine 10records which class loader loaded the class. When a loaded class refersto another class, the virtual machine 10 requests the referenced classfrom the same class loader that originally loaded the referencing class.For example, if the virtual machine 10 loads the class “Volcano” througha particular class loader, it will attempt to load any classes to whichVolcano referred with the same class loader. In this way, thearchitecture of the JAVA language enables a programmer to createmultiple “name spaces” inside a single JAVA application. Each classloader in the executing JAVA application has its own name space, whichis populated by the names of all the classes it has loaded.

The execution engine 18 executes instructions contained in the methodsof loaded classes in “bytecode”, essentially JAVA machine language. TheJAVA language specification describes what is to result from a giveninstruction retrieved from a JAVA method, but a programmer of a JAVAapplication determines the best way of achieving the result usingsoftware, hardware, or a combination of both. The execution engine 18 isan abstraction; JAVA is a programming language capable of simultaneouslyrunning multiple threads, i.e. distinct paths of execution, hence theexecution of each thread can be considered an “instance” of the abstractexecution engine 18. Thus at any given time, there may be multiple“instances” of the execution engine 18.

The execution engine 18 receives a bytecode stream of instructions in athread and executes the thread one instruction at a time. The executionengine 18 executes the actions requested by each thread, and wheneverintended by the JAVA application, sends instructions to the operatingsystem in the code that the operating system recognizes. From time totime, the execution engine 18 might encounter an instruction thatrequests a method written in some other language than the JAVA language,referred to as a “native method.” On such occasions, the executionengine 18 will attempt to invoke that native method by accessing nativemethod libraries 36 through a native method interface 34 (shown in FIG.2). When the native method returns, the execution engine 18 willcontinue executing the next instruction in the bytecode stream.

When the JAVA virtual machine 10 runs an application, it needs memory tostore many items, including information it extracts from class files,objects that the program instantiates, parameters to methods, returnvalues, local variables, and intermediate results of computations. TheJAVA VM 10 organizes the memory it needs to execute a program intoseveral runtime data areas, depicted in FIG. 2. These runtime areas mayinclude a method area 24, a heap 26, one or more JAVA stacks 28, one ormore program counter (PC) registers 30, and one or more native methodstacks 32. Although the same runtime data areas exist in some form inevery JAVA VM implementation, the structural details of these areas areleft to the designers of the VM and may therefore vary considerably fromone JAVA application to another.

Each instance of a JAVA VM 10 has one method area 24 and one heap 26.These areas are shared by all threads running inside the VM 10. As eachthread comes into existence, it receives its own PC register 30 and JAVAstack 28. When the VM 10 runs a method contained in a thread, severalthings happen. First, the value of the PC register is used to tell thenext instruction in the method's sequence to execute. Second, thethread's JAVA stack 28 stores the state of each executing JAVA method ina stack frame, which includes the thread's local variables, theparameters with which it was invoked, its return value if any, andintermediate calculations. When the VM 10 has invoked a method in athread and that method subsequently completes, the VM 10 discards thestack frame for that method from the JAVA stack 28. The state of nativemethod invocations is stored in the native method stack 32 in a mannerdictated by the designer of the JAVA VM 10.

Information about loaded data types are parsed from class files as theyare loaded and stored in the method area 24. A data type refers to theformat in which the data is expressed, e.g. an integer, a float, etc. Adata type could also be an address of an op code within a method or areference to an object on the heap 26. The VM 10 uses the typeinformation stored in the method area 24 as it executes the applicationit is running.

For each data type the VM 10 loads, it should store the following kindsof information in the method area: (1) the fully qualified name of thetype; (2) the fully qualified name of the type's superclass; (3) whetheror not the type is a class or an interface; (4) the type's modifiers;(5) an ordered list of the fully qualified names of any directsuperinterfaces; (6) the constant pool for the type; (7) fieldinformation; (8) method information; (9) all class variables declared inthe type except constants; (10) a reference to class CLASSLOADER; and(11) a reference to class CLASS. Each of these kinds of information iswell known to those in the art who design JAVA virtual machines andprogram in the JAVA programming language.

Referring to FIG. 3, whenever an object 38 is created by a JAVAapplication, memory for the new object 38 is stored in the heap 26.Because there is only one heap 26 inside of any instance of a JAVA VM10, all threads share the heap 26 and because each JAVA application runsinside its own JAVA VM 10, there is a separate heap 26 for every JAVAapplication running. In this manner, one JAVA application cannot affectthe objects 38 in the heap 26 of another application. Two differentthreads 40 and 42 of the same application, however, could affect eachother's heap data, i.e. the objects 38. For this reason, synchronizationof the access to objects of multiple threads must be planned.

The existing JAVA VM 10, as illustrated in FIGS. 1-3 has severaldisadvantages. First, it is inherently redundant. Referring to FIGS. 4Aand 4B, a single computer 44 when running multiple JAVA applications (orother applications that run in a VM) typically creates a separate VM foreach application. Each VM, in turn, generates its own method area, heap,PC register, etc., using a good deal of the resources of the underlyingcomputer. This is true even when each VM is running a separate instanceof the same application where many of the objects created by theapplication will be identical. This is illustrated in FIG. 4B wherethree computers 46, 48, and 50 are running the same application 54through a server 52. In this instance, many of the runtime data areasmay be located on the server 52, creating the same kind of redundancy asseen in FIG. 4A.

The redundancy of existing VM systems translates to a loss in systemspeed for two reasons. First, each VM must use its own resources, i.e.time, to load objects already loaded in other applications. Second, thecombined memory space of all VM applications often bottlenecks systemresources. In many cases, the speed at which an application or series ofsimultaneously running applications may operate defines the upper limitof a system's performance—the number of trades processed, web pagesserved, or billing records updated per second. In other words, the speedat which individually well-tuned processes can operate determines howmuch value that system can provide on a second-to second basis, i.e.lost system speed means lost revenue.

The existing wisdom is that the redundancy and the associated loss ofspeed that results from designing every VM application to run in its ownisolated VM 10 is a small price in exchange for the assurance that oneapplication cannot change or otherwise corrupt the data being used byanother application. In addition, the isolation of applications eachwithin its separate VM ensures that if one application should close, orsuddenly crash, the other applications would remain unaffected. Thepresent inventors, though, came to the realization that there are avariety of applications in which the sharing of data across applicationsmight actually be beneficial. In those instances, the redundancy of theexisting system for running VM applications and the associated loss ofsystem speed would be needless.

With this in mind, FIG. 5 shows an improved system for running VMapplications, which broadly stated may comprise a shared object space100 and a native access layer 102 operably connectable with a pluralityof application programming interfaces (API) 104, 106 of independent VMs,for example VM 110, or other applications such as the C/C++ application112. The access layer 102 permits each application 112, 114, through itsassociated, API 104, 106 to load objects 108 into the shared objectspace 100 where the objects 108 may be read and/or modified by theparticular applications 112, 114. Although in some instances, theindividual applications may duplicate some of the objects 108 stored inthe shared object space 100 within its own respective heap or othermemory area, the shared object space 100 permits an application to storean object 108 in the shared object space 100 instead of its own heap orother memory area, thus avoiding the redundancy of existing VM systems.Access to the objects 108 in the shared object space 100 may besynchronized for controlling access to shared objects in a heap bymultiple concurrently running threads. Further, the shared object space100 will store an object 108 so long as a thread of any connectedapplication is using the object 108. In this manner, even if theapplication that placed a particular object in the shared object space100 closes or crashes, that object will still be available to otherapplications as necessary. Thus the shared object space 100 permitsmultiple applications running simultaneously on a system or network toenjoy the stability of existing VM systems, while providing asubstantial boost in performance.

The shared object space 100 is accessible to an application through thenative access layer 102. Thus a JAVA application or other objectoriented application will recognize the shared object space 100 assimply another resource accessible through the native methods interfacethat already exists in JAVA applications and other object-orientedapplications. Once accessed, all the functionality of the shared objectspace 100 will be instantly accessible to the connected application.Further, the shared object space 100 does not need to be tied to aparticular VM, but instead is backwards compatible with any individualVM, whether it is a standard JAVA VM provided by Sun Microsystems or acustomized VM of a particular business, and forwardly compatible withany VM including improvements that have yet to be developed. Thus theversatility of the shared object space 100 can not be overstated. Theversatility of the shared object space 100 is furthered by itscompatibility with a wide variety of application interfaces. As can beseen in FIG. 5, the native access layer 102 provides access to theshared object space 100 by both JAVA applications and C or C++applications. It should be understood that these examples areillustrative only, and that the native access layer 102 could provideaccess to the shared object space 100 by a number of other applicationtypes, whether object-oriented like JAVA applications or commandoriented like C or C++.

The advantages of the shared object space 100 are readily apparent,particularly with respect to applications that benefit from the abilityof multiple, simultaneously running applications to update a sharedobject rather than simply read or copy a shared object. One suchapplication might be online trading. As the popularity of online tradingincreases, trading exchanges are faced with ever-growing volumes ofmarket data and concurrent trader activity. Systems that were built tohandle moderate volumes now have to handle thousands of traders andbillions of dollars in daily transactions. Such systems have toaccommodate huge spikes in demand. For instance, a single trade mayrequire thousands of traders to be notified. Many traders watch forthese price changes, then jump in to sell or buy very quickly, causingeven more notification demand and more trading volume. The faster atrading system reacts to changes, the more transactions an exchange canexecute, increasing its commissions while maximizing trader satisfactionwith the service.

Another example of the utility of the shared object space 100 might beits potential in improving speed of computerized activity in thetelecommunications industry. Modern telecommunication networks have toprocess vast amounts of data very quickly. Every time a call is placed,for example, an application needs to access the customer's subscriptioninformation, apply any special discounts that may be applicable, monitorthe call duration and establish a rate based on the time and distance tothe terminating number. Given that the number of such calls can run intothe thousands at any given moment, a memory based data sharing facilityis a necessity. In the past, such telecommunications applications havebeen written from scratch in C at enormous expense. The availability ofan off-the-shelf shared memory component that provides a shared objectspace 100 makes it possible to write such systems in the JAVAprogramming language or another object-oriented language more quickly,cheaply, and with less risk.

Yet another example of the utility of the shared object space 100 is itspotential use in large scale internet applications. Large internetcontent syndication and portal applications depend on fast caching forscalability. The shared object space 100 provides an ideal cachingfacility for HYPERTEXT MARKUP LANGUAGE (HTML) and EXTENSIBLE MARKUPLANGUAGE (XML) program fragments, XML DOCUMENT OBJECT MODEL (DOM)program interfaces and streams, HYPERTEXT TRANSFER PROTOCOL (HTTP)session information, and JAVA Database Connectivity (JDBC) queryresults. It can also hold very fast page request queues and otheroperational data structures. The shared object space 100 may includemulti-language support which may be exploited when connected to webservers, servlet engines, content management suites, and XML transcodersto speed up every phase of a sites operation.

In use, the shared object space 100 may be one element in a largercomputing system 101. Specifically, it is anticipated that the sharedobject space 100, along with its associated native access layer 102 maybe used in conjunction with a console 118, an administrative processor120, disk storage 122 and a display 124 suitable for displaying systemstatistics. The console 118 is used to configure and start the system101 which may comprise a system manager 126, the shared object space100, and the native access layer 102. The system manager 126 creates andinitializes the shared object space 100, collects garbage, gathersstatistics, and logs both system and user-defined events. Once thesystem 101 has been started, the system manager 126 can also be used tobrowse the shared object space 100, enable statistics collection fromindividual objects, and display the statistics graphically for analysis.

The system 101 is preferably stored on a disk 122 in a defaultdirectory, e.g. “defaultSystem”, that holds the system's configurationfile and log file. The system 101 may be included on an executablestorage media such as a compact disk that include an installation toolthat may be used to create the requisite directories on the disk 122.Additional custom system directories may also be installed on the samedisk 122 as desired. Preferably, the system 101 includes a number ofdefault tools that operate on the default system; however the console118 and a command line utility may allow the user to specify a differentsystem.

To make use of the system 101 and its shared object space 100, thesystem 101 includes a library file in the default directory. JAVAapplications should include a reference to this library (e.g.productdir/lib/gemfire.jar) on its CLASSPATH. On systems utilizing theWINDOWS operating system, the library may be made available by addingproductDir/bin to PATH and on systems having the Solaris operatingsystem, the library can be made available by adding productDir/lib toLD_LIBRARY_PATH. An application process connects to the system 101 bymaking a call that contacts the system manager 126, such asGemFireConnection.myConn=GemFireConnection.getinstance (“Gemfire”). Thesystem manager 126 then returns information that enables the applicationprocess to map the shared object space 100 into its address space.

Each system 101 preferably maintains a global name space 116 in theshared object space 100. The name space 116 provides a fast objectregistry in which applications can register and look up “root” objectsby name. Objects that are referenced from this name space are protectedfrom garbage collection. Once connected to the system 101, anapplication can look up shared objects in the name space 116 with acommand such as

-   -   Stock myStock=(Stock)    -   myConn.lookup (“GSI”)        A shared object like myStock always represents a current shared        value; that is all threads in all VMs always see the same field        values, just as all threads in a single VM see the same volatile        field values for an object in that VM. The statement    -   myStock.getPrice( )        for example, might return the price most recently set by a local        or remote thread, while the statement    -   myStock.setPrice (34)        immediately updates the shared view of myStock's price. Because        these fetches and updates incur no disk or network overhead,        they are much faster than the same operations implemented        through mechanisms like the JAVA Remote Method Invocation API        (RMI) and they outperform JDBC calls by an even wider margin.

The system 101 may include a Class Enhance tool that prepares anapplication class for sharing by modifying the class's bytecodes toprovide transparent instantiation in shared memory and automaticread-through and write-through for field access methods. By default, allfields may be shared, but a user may establish more selective policiesby providing an XML description of the fields to be shared in eachdomain class. Once a class is enhanced, making an object of that classautomatically puts the object into shared memory.

Referring to FIGS. 6 and 7, the system 101 may support two methods ofsharing objects, copy sharing and direct sharing. An object 128 that iscopy shared is allocated twice, once in the local memory of anapplication and again in shared memory 100. FIG. 6 shows an example of acopy sharing method where application A creates an object 128 in itslocal address space. The object 128 is shared by putting it into theshared name space 116. At this point, the object 128 is not immediatelywritten to a field in the shared object space 100; instead the object128 is written to shared memory 100 only after a user “flushes”, i.e.updates the object to a new version, for the first time. Once an object128 is written to shared memory, application B is able to copy theobject 128 to its local memory by accessing the shared object 128 byname in the shared name space 116. Application B may modify the copy ofthe object 128 obtained from shared memory, and may also flush to updatethe shared memory copy of the object. If application B wishes to see themost recently updated version of the object 128, a refresh command maybe used.

FIG. 7 shows an example of a direct sharing method, which is a one-spacemodel where some of all of the non-static fields of the shared object128 reside only in shared memory. Static fields may be kept in the localheap of an application's VM for performance reasons. An assignment to afield of a directly shared object 128 is immediately visible to threadsof other applications and each application is able to write to theshared object. When the field is read, the current state in sharedmemory 100 is returned; there is no need to refresh the local memory.

FIG. 8 shows another system 201 that includes a shared object space 200within a first JAVA VM 202. The first JAVA VM 202 may include all theelements of a typical JAVA VM as previously described, i.e. a methodarea, a class loader, an execution engine, etc. The heap of the firstJAVA VM, however, acts as the shared object space 200 so as to beaccessible by the execution engine 204 of a second JAVA VM 206. In thesystem 201, the first instance of an application may initiate a VM whoseheap performs as a shared object space for subsequent instances ofapplications operating on the same computer. The shared object space 200may have all the functionality of the shared object space 100 previouslydescribed.

FIG. 9 shows another system 301 in which a shared object space 300resides on a server 302 interconnecting independent computers 304, 306,308 operating on the same or different platforms. Each computer 304,306, and 308 is running a VM instance of a single application that readsand/or writes to data in a database on the server 302. For example, theserver 302 may include a dynamic database for stock prices in a tradingscenario where the connected computers 304, 306, and 308 may be used tocomplete stock transactions through the server using a uniform softwarepackage.

As stated previously, when multiple threads from multiple applicationsare sharing objects in a shared object space, access to the objectsshould be synchronized. FIG. 10A illustrates this necessity. In thisfigure, application 303 is running in a VM 305 while application 307 isrunning in another VM 309. Both VM 305 and VM 309 are sharing the sharedobject space 300 that is storing a shared object 310. In this figure,application 303 is simultaneously running two threads, thread 312 andthread 314, both of which are calling shared object 310. At the sametime, application 309 is running a thread 316 which also is calling theshared object 310. Absent synchronization, each thread 312, 314, and 316could all access the shared object and make simultaneous, possiblyconflicting changes to the object 310 without any knowledge of eachother's changes.

Also, as stated previously, existing methods provide for synchronizationof multiple threads in a single application accessing a shared object ina single VM. Extended synchronization techniques, as described herein,may be used to provide synchronization for concurrent access to objectsin shared memory by multiple applications illustrated in FIG. 10B.

In FIG. 10B, a shared object space 300 stores objects O, P, Q, and R.Each of these objects includes an object header 320. Each object header320 may include a lock info field 322 which is used to indicate whethera thread of an application has locked that object. The lock info field322 may contain either a “cheap lock” or a reference to a “lock node”,i.e. an “expensive lock.” A “cheap lock” directly encodes the identityof the application and the thread that owns the lock by inserting avalue into the lock info field 322 unique to the thread of thatapplication. (The value “0” may be used to indicate that an object isnot locked by any thread of any application.) When thread A ofapplication 326 seeks to acquire object O, for example, thread A checksthe header of object O to test whether the value in the lock info field322 is “0”, representing that it is not locked. If the value is “0” thenthread A 324 substitutes its unique number in the header of object O andacquires the lock with a “cheap lock.”

This compare and swap informs subsequent threads that wish to acquireobject O that the object is “locked” and these threads will wait. Thiscompare and swap is preferably “atomic” in nature, meaning that theissued command(s) is performed in such a manner that there is nopotential for another thread or otherwise to lock the object in theinterim, especially when the command is executed by the processor. Inmany cases, the swap is performed in a manner internal to themicroprocessor, and is accordingly a very efficient mechanism. Forexample, if thread B 328 of application 330 seeks to acquire the objectO while thread A 324 already has it, thread B will test to see whetherthe lock info field 322 is “0”. The test will fail and thread B willrecognize that thread A has the object because of the number in theheader. At this point, thread B does several things. Thread B makes twoentries in a lock table 332 called “lock nodes” 336 and 337. The locknode 336 is unique to thread A and the lock node 337 is unique to threadB. Also, thread B updates the “cheap lock” of the lock info field 322 toan “expensive lock” that contains a reference to the lock node 336 inthe lock table 332. Thread B then goes to sleep waiting on its lock node336. When thread A is finished it notifies the lock manager 334 whichremoves the lock node 336 from the lock table and swap's B's “expensivelock”. i.e. a reference to the lock node 337, into the lock info field322 of the object's header. Thread B thereby gains control of theobject.

A lock node, such as 336 and 337, is an internal object, not visible tothe application. When a lock node is created, it is added to the locktable 332. If a thread of an application wanting to acquire the lockmust wait for another thread to release the lock, it waits on the uniquelock node object representing its lock request. The lock table 332 holdsinstances of lock nodes. A given lock node in the table representseither a thread that currently holds a lock or a thread that is waitingto acquire a lock. The lock node contains information pertaining to thevirtual machine that has or wants the object, as applicable, the threadthat has or wants the object, as applicable, and the object had orwanted, as applicable. When the lock manager 334 successfully grants alock to a thread by setting the target object's lock info field 322 tobe a reference to the lock node representing the waiting thread, usingthe compare and swap technique, it signals the lock node. The waitingthread then gets the object and proceeds.

All of the aforementioned activities of thread B occur without anyeffect on thread A. Stated differently, thread A is unaware of anythingthat B is doing and hence is not slowed down by thread B's activities.When thread A is finished and seeks to release the lock on object O, itwill check the lock node 336 and see that there are one or more threadswaiting for access to the object O. A first assumes that the lock isstill a “cheap lock” and does a compare and swap. If the lock has beenupdated to an expensive lock, its value is no longer in the lock infofield, so the test and swap will fail. In that case, two implementationsmight occur.

In the first implementation, the object's lock info field is set to “0”and the lock manager is signaled that there may be another lock node inthe lock table that can be granted the lock. (This is generally fasterfor the application thread). The lock manager 334 will then consult thelock table to see which thread has priority, in this case thread B, andtherefore grant thread B access to object O, at which point thread B's“expensive lock” will be inserted in the header of object O, etc. Thesecond implementation is that the thread, i.e. A, does the work ofdetermining the next owner of the lock and atomically changes theobject's lock info field 322 from a reference to its lock node to areferenced to the next owner's lock node. This eliminates the need for alock manager, at the expense of making the application slower.

The following is an example of a JAVA program fragment that might beused to invoke the procedures described above:

Lockservice.synchronize (    anObject,new Runnable ( ) {      Lockservice.notify (anObject);       Lockservice.wait (anobject);   } );

The following is an example of a C fragment that may be used to invokethe procedures described above:

-   -   Status=gfacquireLock (employee)    -   doWork    -   gfReleaseLock (employee)

The foregoing example illustrated the process that would occur if twothreads were contending for access to the same object. Obviously theremay be quite a few threads seeking access to an object simultaneously,and in that event the foregoing procedure will control the priority ofaccess in an orderly fashion through the lock table 332 which recordsthe relative priority of access to an object between multiple threads.In the foregoing example, access to an object by multiple threads isgranted in order of the requests, i.e. first come, first served. Othersystems may be used. For example, some systems may provide for threadsto be indicated as priority threads whose function is of some criticalimportance, and their place in the lock table accordingly bumped up. Insome cases there is no guarantee to priority of access, so that ifthreads B. C. and D all try to obtain a lock while thread A has it,thread B may not be next in line even if it were the first to try toobtain the lock with respect to threads C and D.

The advantage of the foregoing system is a considerable boost in speed.For example, when there is no contention for an object at the time athread is trying to acquire it, the object may be obtained by a threadin as little as 10 microseconds. Where there is contention, however, itmay take more than 100 microseconds to acquire the object after it hasbeen released. Thus the ability to quickly detect whether or not thereis contention for an object permits a thread to acquire the object bythe quicker method.

FIG. 10B shows that object O is the parent of objects P and R and objectP is the parent of object Q. Objects O, P, Q, and R each have headerswith a lock info field 332. Therefore, threads are able to obtain objectQ, for example, without needing to lock any of the other objects,freeing them for use by other threads.

Many processes or threads in an application are contingent upon theoccurrence of an event. For example, when a user of a word processingprogram presses a font button, such as an italics button, theapplication must respond appropriately. When an online buyer clicks a“proceed to checkout” button or an “enter” button after typing in acredit card number for a purchase, the web server must respondappropriately by either loading another screen, verifying the creditcard account information, etc. In each of these instances, the eventthat triggers the response is uncertain, i.e. it may or may not occur.To handle these contingencies, many object oriented programs use“listeners”, which are defined as objects that are notified when anevent has occurred. There exist many types of listeners, such as anActionListener (which defines a method to receive an action event), aContainerListener (which defines two methods to recognize when acomponent is added to or removed from a container), a KeyListener (whichdefines three methods to recognize when a key is pressed, released, ortyped), and a WindowListener (which defines seven methods to recognizewhen a window is activated, closed, deactivated, deiconified, iconified,opened, or quit). This list is not exhaustive as there are several otherpredefined types of listeners, and others may be customized as the needarises by using the EventObject utility to define a desired event thatis to be listened for.

To attach a listener to an object, that object registers a listener witha command of the general form

-   -   Public void add TypeListener( )        in which Type is the name of the event. At that point, the        listener “listens” to the object to detect the occurrence of the        event defined in the listener.

Listeners consume a relatively large amount of system resources, and theuse of multiple listeners in a computing system tends to slow the systemdown. For that reason, it is often desirable to program an applicationusing as few listeners as possible while still achieving the functionsof the application

Referring to FIG. 11, the shared object space 400 permits multipleapplications, such as 402, 404, 406, and 408 to each listen for an eventin a shared object such as 410 in a highly efficient manner by placinglisteners 412 and 414 into the shared object space 400 as well as theobject 410. For example, Applications 402, 404, and 406 may each beprogrammed to listen for the same event in object 410. In the systemdepicted in FIG. 11, each of these applications 402, 404, and 406 neednot create its own separate listener, but instead may share a singlelistener. In addition, a single application, such as application 404,may have more than one listener, such as 412 and 414 attached to theshared object 410. Thus a system in which listeners are shared bymultiple applications improves over existing systems by utilizing lesssystem resources and increasing the speed at which the multipleapplications may operate.

It should be understood that other implementations of shared listenersmay have each listener associated with only one application running in asingle virtual machine, such as that shown in FIG. 12. Referring to thisfigure, listeners are a common pattern implemented by an applicationwith two main roles involved—an event producer and an event listener.The event producer typically holds a set of listeners and provides amethod such as addListener( ) where the listener is an object thatimplements an application-defined listener interface. The listenertypically either implements this interface directly, or with ananonymous inner class.

In the situation where a listener is implemented in an applicationrunning in its own VM, with no shared object memory, this common patternrequires no special language support. When an event is produced, theevent producer simply iterates over its collection of listeners andinvokes the appropriate method in each one. For example, assume that asingle VM has a listener where TradeFloor is the event producer, whichinvokes the listener's stockOffered( ) method, as defined by a listenerinterface OfferListener. Trader is the listener—it implements andlistens for stockOffered( ) using the following code:

public class TradeFloor {    Collection listeners = new ArrayList( );   public void addOfferListener( OfferListener listener ) {      listeners.add(listener);    }    ...    // Stock is being offered   Iterator listenersIterator = listeners.iterator( );    while(listenersIterator.hasNext( )) {      ((OfferListener)listenersIterator.next( )).       stockOffered(ticker, price );    }    ... } public class Trader {  TradeFloor floor =TradeFloor.getInstance( );  public Trader( ) {  ...   floor.addOfferListener( new OfferListener( ) {    public voidstockOffered( String ticker, int price ) {     // Just got notified thatstock is offered    <do stuff>    } }); } }

When the TradeFloor is instantiated, it initializes listeners to be anempty ArrayList. When a Trader is instantiated, it looks up thesingleton instance of TradeFloor and adds itself as a listener (using aninner class). When the TradeFloor has a stock offered, it iterates overits listeners to send stockOffered( ). This invokes code in classTrader.

In the system shown in FIG. 12, however, the event may occur in adifferent VM from where a listener was registered, which precludes asimple method invocation from the event producer to the listener. Theforegoing code should therefore be changed to provide a mechanism thatallows applications to implement the listener pattern such that the codethat produces the event (in this case, the TradeFloor) executes in oneVM, and listeners can be invoked in one or more other VMs. For example,the line “Collection listeners=new ArrayList( )” in the foregoing one-VMexample could be changed to “Collection listeners=newSharedListenerList( )” to provide the desired functionality. In thismulti-VM example, the SharedListenerList (which is a shared object)should be the same shared object across all VMs. This usually occursnaturally by having the object that holds it be a common shared object.TradeFloor, for instance is a shared object, and its instance variablelisteners are part of its shared state. All uses of the shared instanceof TradeFloor will share the same listeners. TradeFloor.getInstance( )performs a lookup in the shared namespace. Further, the classes thatdefine the listener interface(s), listener method argument types, returnvalues and exceptions must be loadable across all participating VMs.

The systems shown in FIGS. 11 and 12 permit a listener to distinguishnot only when an event occurs in object R, but also what particularapplication caused that event. Because any given application, such as402, 404, 406, and 408 may access an object, such as object R 410 forinstance, by swapping into the object header's lock info field 422 avalue unique to that particular application, the listener may includecode that allows it to identify the particular application that causedthe event that it is listening for. Because the lock info field 422 maybe any desired bit length, the system of FIG. 11 can accommodate anydesired number of applications, each of which can then be individuallyidentified by the listeners such as 412 and 414 when causing an event.In order to implement this feature in the manner just described, thelistener's code could be customized in a variety of ways. The listenercould be modified to listen for an event defined as the conjunction ofthe event or events typically associated with that listener (e.g. thedepression of a key for a KeyListener) and any change in the lock infofield 422 so that any time a key is depressed, the listener detects theevent and notes the application that caused the event. Alternatively, ifthe value of the lock info field 422 is known for each of theapplications permitted to access the shared object space 400, then thelistener may be modified to listen for an event defined as theconjunction of the event or events typically associated with thatlistener (e.g. the depression of a key for a KeyListener) and the changein the lock indicator value 422 to a specific identifier in order tolisten for an event taken by a specific application.

Many other modifications to the code of a listener are available to theprogrammer to permit the association of an event with the application(or possibly applications) that caused the event. For example, if theprogrammer has the ability to modify the code of the applicationsaccessing the shared object space 400, another method may be to simplyrequire the applications to include an identifier in the argument of thechange they make to the object, such as 410, and customize the listenerto include that value in its argument once it detects that the event itis listening for has taken place.

Whatever particular modification is chosen by the programmer, theability to associate an event with the application that caused thatevent may be of considerable advantage. For example, this feature couldbe used to collect statistics as to activities of all applications usingthe shared object space 100. Alternatively, where desired, the responseof one particular application may be keyed to a particular action takenby another application, or one of a subset of the total number ofapplications using the shared object space 400.

The terms and expressions that have been employed in the foregoingspecification are used therein as terms of description and not oflimitation, and there is no intention, in the use of such terms andexpressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that the scope of theinvention is defined and limited only the claims that follow.

1. A computer system for concurrent operation of plural applications,said computer system comprising: (a) a memory including a shared objectspace capable of storing at least one shared object and a listener; (b)a shared object stored in said shared object space and accessible to atleast two applications so that at least a first application is capableof causing an event in said shared object, said first applicationrunning in a first virtual machine; (c) a listener attached to saidshared object and operably associated with a second application runningin a second virtual machine, said listener listening for said event andnotifying said second application when said first application has causedsaid event; and (d) said listener being able to identify an applicationother than said second application as causing said event.
 2. The systemof claim 1 where said listener is located in said shared object space.3. The system of claim 1 where at least two applications are capable ofcausing said event.
 4. The system of claim 1 further comprising a secondlistener located in said shared object space and attached to said sharedobject.
 5. The system of claim 1 where at least one of said virtualmachines is a Java virtual machine.
 6. The system of claim 1 where saidshared object space is linked to at least one application by a nativemethod interface enabling said application to utilize a method native tosaid application in interacting with said shared object.
 7. The systemof claim 6 where said system includes a default directory with a nativelibrary.
 8. The system of claim 1 including a non-object-orientedapplication.
 9. The system of claim 8 where said non-object-orientedapplication is a C application.
 10. The system of claim 1 where accessto said at least one object by said plural applications is synchronized.11. The system of claim 1 where said plural applications implement astock trading system.
 12. The system of claim 1 where said at least oneobject is copy shared among said plural applications.
 13. The system ofclaim 1 where said at least one object is direct shared among saidplural applications.
 14. The system of claim 1 including a systemmanager that analyzes information pertaining to the operation of saidshared object space.
 15. The system of claim 1 including a global namespace in said shared object space.
 16. A computer system for concurrentoperation of plural applications, said computer system comprising: (a) amemory including a shared object space capable of storing at least oneshared object and a listener; (b) a shared object stored in said sharedobject space and accessible to at least two applications so that atleast one application is capable of causing an event in said sharedobject, said application running in a virtual machine and said sharedobject containing a header capable of containing an identifier of theapplication that caused said event; (c) a listener attached to saidshared object and operably associated with at least one applicationrunning in a virtual machine, said listener listening for said event andnotifying an associated application not causing said event of anoccurrence of said event; and (d) said listener being able to identifyfrom said header an application other than said associated applicationas an application causing said event.
 17. The system of claim 16 wheresaid listener is located in said shared object space.
 18. The system ofclaim 16 where at least two applications are capable of causing saidevent.
 19. The system of claim 16 further comprising a second listenerlocated in said shared object space and attached to said shared object.20. The system of claim 16 where at least one of said virtual machinesis a Java virtual machine.
 21. The system of claim 16 where said sharedobject space is linked to at least one application by a native methodinterface enabling said application to utilize a method native to saidapplication in interacting with said shared object.
 22. The system ofclaim 21 where said system includes a default directory with a nativelibrary.
 23. The system of claim 16 including a non-object-orientedapplication.
 24. The system of claim 23 where said non-object-orientedapplication is a C application.
 25. The system of claim 16 where accessto said at least one object by said plural applications is synchronized.26. The system of claim 16 where said plural applications implement astock trading system.
 27. The system of claim 16 where said at least oneobject is copy shared among said plural applications.
 28. The system ofclaim 16 where said at least one object is direct shared among saidplural applications.
 29. The system of claim 16 including a systemmanager that analyzes information pertaining to the operation of saidshared object space.
 30. The system of claim 16 including a global namespace in said shared object space.